Light emitting diode (LED) strings have been used as decorative lighting and have become an important part of daily life. The properties of LEDs, such as low operating voltage and power, small size, long lifetime and extended stability, make them desirable as lighting sources. Moreover, LEDs do not generate a substantial amount of heat and are safe for daily operation.
In conventional LED strings, LEDs are connected either directly to a standard household alternative current power source or through an AC to DC converter. Directly connecting an LED string to a household AC power source is inexpensive, but generates 60 Hz glitter because the LEDs in the light string only work under positive half-waves of the alternating current source. Moreover, when LEDs are connected to an alternating current power source, the lifetime of the LED is shortened, due to the negative voltage applied by the negative half-waves. The use of AC to DC converters with each LED light string becomes substantially more expensive.